The objective of this proposal is to investigate mechanisms of swallow gene function in Drosophila, as a means of understanding cytoplasmic organization and its role in early development. The swallow gene participates in the subcellular localization of several mRNAs during Drosophila oogenesis, and may also play a role in regulating nuclear divisions during early embryogenesis. In order to advance our understanding of Swallow function, the following studies will be initiated: (1) Homologues of swallow will be cloned from related species, analyzed for conserved regions, and tested for their ability to provide normal swallow function in Drosophila melanogaster. (2) Immunoprecipitations will be used to identity binding partners of Swallow and to test the hypothesis that Swallow forms homodimers. (3) Site-directed mutagenesis will be used to construct and test modified Swallow proteins in transgenic flies. This will allow identification and characterization of functional motifs in the Swallow protein. These studies are designed to answer some basic questions regarding swallow function. For example, which regions of the swallow protein are important for RNA localization? For early embryogenesis? How is the function of swallow in oogenesis related to its function in embryogenesis (if at all)? What other proteins does Swallow interact with to localize RNAs? As an integrated whole, these experiments will provide valuable information on the function of Swallow protein. This research is of particular interest because it is becoming clear that many characteristics of subcellular localization are highly conserved. The subcellular localization of macromolecules is likely to be an important event in any cell that has an established polarity, and information gained from the proposed experiments will improve our understanding of subcellular organization in general.